What does it mean for it to go into error mode--does it actually lock you out and quit functioning? If so, that's just crazy.
All Suunto computers go into error mode (stop calculating stops) when you go above the ceiling for more than 3 minutes. IIRC it will continue to display depth and time but that's it.
What Rob said. When it goes into error mode, it essentially turns into a bottom timer in the middle of your dive.